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Convergence error of water activity
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Topic: Convergence error of water activity (Read 2065 times)
leizheng41
Contributor
Posts: 3
Convergence error of water activity
«
on:
July 07, 2018, 04:57:36 AM »
Hi!Thank you for reading this question.
I was using Phreeqc to simulate the oxidation process of Pyrite in 158 steps, but a convergence error of water activity occurred in the 59th step. Does anyone know what the reason is?
Thanks in advance!
Here is my code.
------------------------------------------
TITLE 1
EQUILIBRIUM_PHASES 1
Pyrite 0 0.1612
Calcite 0 0.0232
REACTION 1
O2(g) 1
158 moles in 158 steps
SOLUTION 1
temp 13
pH 7
pe 4
redox pe
units mmol/kgw
density 1
-water 1 # kg
SELECTED_OUTPUT 1
-file D:\Program Files (x86)\USGS\Phreeqc Interactive 3.4.0-12927\Lei\selected_output_1.sel
-totals S(6) Fe Ca C(4)
-equilibrium_phases Pyrite Calcite
END
-------------------------------------------------------------------------------
I got following error after running the code above.
-------------------------------------------------------------------------------
Reaction step 59.
WARNING: Maximum iterations exceeded, 100
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Trying smaller step size, pe step size 10, 5 ...
WARNING: Maximum iterations exceeded, 200
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Trying reduced tolerance 1e-16 ...
WARNING: Maximum iterations exceeded, 200
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Trying increased tolerance 1e-14 ...
WARNING: Maximum iterations exceeded, 200
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Trying diagonal scaling ...
WARNING: Maximum iterations exceeded, 200
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Trying diagonal scaling and reduced tolerance 1e-16 ...
WARNING: Maximum iterations exceeded, 200
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Trying scaling pure_phase columns 1e-10 ...
WARNING: Maximum iterations exceeded, 200
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Trying scaling pure_phase columns and diagonal scale 1e-10 ...
WARNING: Maximum iterations exceeded, 200
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Trying delay removal of equilibrium phases 1 ...
WARNING: Maximum iterations exceeded, 100
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Trying increased scaling 1e-09 ...
WARNING: Maximum iterations exceeded, 200
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Skipping optimize equations for first 5 iterations ...
WARNING: Maximum iterations exceeded, 100
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Adding inequality to make concentrations greater than zero.
WARNING: Maximum iterations exceeded, 100
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Trying reduced tolerance 1e-17 ...
WARNING: Maximum iterations exceeded, 200
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: Trying reduced tolerance 1e-18 ...
WARNING: Maximum iterations exceeded, 200
WARNING: Numerical method failed with this set of convergence parameters.
WARNING: The program has failed to converge to a numerical solution.
The following equations were not satisfied:
ERROR: A(H2O) Activity of water has not converged. Residual: 7.207689e-06
-----------------------------------------------------------------------------------------------------------------
Logged
dlparkhurst
Top Contributor
Posts: 2736
Re: Convergence error of water activity
«
Reply #1 on:
July 07, 2018, 05:53:23 AM »
158 moles of O2 is unreasonable, and the numerical method failed.
Logged
Cauchy
Contributor
Posts: 8
Re: Convergence error of water activity
«
Reply #2 on:
June 03, 2019, 04:56:14 PM »
Hello, I have kind of same error.
Could one help ?
Logged
dlparkhurst
Top Contributor
Posts: 2736
Re: Convergence error of water activity
«
Reply #3 on:
June 03, 2019, 06:29:51 PM »
Consider your calculation more carefully. You are adding 158 mol of O2 to 1 kg of water. Note you only have 0.16 mol of pyrite, and a kilogram of water has only 55.5 mol of O for comparison. By step 58, the pyrite is long gone, and the calculated partial pressure of O2(g) is over 30000 atm. I don't think your REACTION is reasonable.
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Convergence error of water activity